I guess you haven't seen the photographs of SASR on patrol in Somalia then?
Have a guess what vehicle they used...
Sorry mate, I don't mean to be rude, but you are wrong in SO many ways...
1. The reserves are NOT the "primary" defence against invasion. The regular Army, RAN and RAAF are.
2. Under the old "Defence of Australia" strategic guidance, the reserves primary role was to provide a basis for the expansion of the Army to meet "wartime" commitments.
Basically, the reserve elements (2nd Division) would have provided the basis for a significant enlargement of Australia's Army. 1x Reserve battalion would split (in effect: provide the "original rifle company" and part of the Admin company for the new unit) into the basis of 2,3 or 4 "frontline" battalions depending on need etc.
3. The Reserve "Armoured Corps" Units used to be structured and equipped to provide an APC capability for the Brigade they were attached to. Their role changed in the late 90's early "naughties" (2000 onwards) to providing a recon/surveillance capability. Their previous troop carrying role was removed because of the introduction of Project Bushranger which provided specific transport capability for the battalions themselves.
All the reserve Armoured Corps units from 2000 onwards were therefore effectively intended to provide the same sort of capability as the ASLAV equipped 2nd Cavalry Regiment and 2/14 Light Horse (Queensland Mounted Infantry) (Reconnaisance) Regiment's.
The difference being that the Reserve units are equipped with the M113 and the Regular units equipped with the ASLAV (variants of both vehicles ALSO equipped each unit. The generic name is intended to keep things simple) however the regular units have the time available to adequately "qualify" on the modern capabilities as well as conduct individual and collective training and the Reserves do not.
With respect to your other comments, PLENTY of other vehicles can be "up-armoured" (including the Land Rover). The vehicle is not the important issue, but rather the capability the particular unit (and it's individual soldiers therein) can generate. A soldier is currently trained as a driver on an ASLAV vehicle (IET drivers course) in 6 weeks. In a wartime scenario, I can only imagine that this would be significantly reduced...)
The Land Rover RSV's are to be replaced in the next few years, but they can mount the weapons you see as necessary if required. Perhaps you are not familiar with the British Land Rover "WMIK" variant?
http://upload.wikimedia.org/wikipedia/commons/9/9c/Len02.jpg
The current "typical" configuration of the Land Rover RSV's is for rthem to mount: 1x F-89 Minimi 5.56mm LSW and 1x MAG-58 7.62mm GPMG. I am sure that "heavier" weapons could be carried without a significantly greater effort, if necessary.
As to the "persistence" of the vehicle, a Land Rover RSV can carry 3 days worth of kit, fuel, stores etc. An M113 is struggling to do so...